Sliding metal contact surfaces, and in particular cylinder liners of internal combustion engines, present a difficult problem of lubrication. Lubricating oil presented to a hard smooth cylinder liner surface is eventually scraped off such surface by tightly interengaging piston rings, thus preventing wetting and retention of an oil film. However, modifications to allow buildup of an oil film can lead to undue oil comsumption by exposure to the combustion process. The prior art has attempted to controllably retain the lubrication oil in pores created in the bearing surface by grit blasting but, due to the viscosity of the oil, the reserve of oil in the pores is diminished by dragout.
Thus, the art has turned to lubricants, other than oil, to promote improved friction-free contact. Such lubricants have included graphite, MoS.sub.2, and organic resins. U.S. Pat. Nos. 3,075,279; 2,691,814; 3,073,761; 3,500,525; and 2,622,993 illustrate attempts to bond these lubricants to the bearing surface by using pressure to achieve adherence on an unpitted surface. However, the adherency has not always been successful and such treatment is not suitable to internal combustion engines where close tolerances would be affected by such coatings.
Better adherency has been sought by the prior art by way of selecting lubricants that can be heat fused to the bearing surface which in some cases has been pitted by grit blasting or etching (see U.S. Pat. Nos. 3,341,348; 3,054,649; and 2,807,511). However, these coatings by necessity are thick and require the additional expense of stripping to expose the bearing surface.
What is needed is a treatment for sliding metal contact surfaces which provides a ready supply of lubricating material at the surfaces without the necessity of bonding the material. Such supply should be self-regulating and not require stripping to obtain some metal bearing. Furthermore, such material should be compatible with oil lubrication while preventing an undue buildup of a lubricating film.